A bus-sized, 6.5-ton, 20-year-old NASA climate satellite that is falling out of orbit is likely to hit Earth on Friday, but nobody can say where. The chances are slim that anyone will see any of the Upper Atmosphere Research Satellite’s 26 assorted pieces that are expected to survive re-entry into the atmosphere. The chances that someone on the planet will be hit by one of those chunks are 1 in 3,200.

The chance that any particular person (in other words, you) will be hit is infinitesimal: one in trillions, the National Aeronautics and Space Administration says.

But that hasn’t stopped a flurry of excitement among space enthusiasts who track satellites and a welter of giddy articles about the possible risks.

FoxNews.com is offering a widget that will allow readers to track the satellite’s progress in real time. Paddypower.com, an Irish gambling website, is taking bets on where debris will land. Odds of at least one piece landing in Ireland were 66 to 1, for example.

A poll item on ABC News’ website asked readers where they thought UARS would crash. Possible answers were “Harmlessly in the ocean,” “In mountains or open plains,” or “My house!” As of Wednesday afternoon, “My house!” was leading “In mountains or open plains” by a margin of 2 to 1.

“It’s business as usual for us here,” said Maj. Michael Duncan, deputy chief of space situational awareness at the Joint Space Operations Center of U.S. Strategic Command at California’s Vandenberg Air Force Base, which is tracking the falling satellite for NASA (along with 22,000 other, mostly man-made orbiting objects). “The UARS re-entry hazard is being overhyped,” said Don Kessler, a retired NASA orbital debris researcher.

NASA scientists already know a lot about how UARS, which was placed into orbit by astronauts on the shuttle Discovery in 1991 and was decommissioned in 2005, is likely to meet its end.

The satellite, which monitored ozone and other chemicals in the upper atmosphere for 14 years, is slowing because it now is in low orbit, where it encounters resistance from the upper atmosphere, NASA space-debris scientist Mark Matney said. As the density of the atmosphere increases, its pieces eventually will break up, lose speed and make their fiery fall.

Forecasters expected that to happen around 3 p.m. PST Friday, give or take a few hours, Duncan said.

According to NASA, the pieces that could hit Earth – mostly titanium, beryllium and stainless steel, and weighing as much as about 300 pounds – will be strewn across a path 500 miles long.

Matney said the chunks, once bulkhead fittings, fuel tanks and the like, will fall as “oddly shaped pieces of metal” and may be charred or mangled. NASA has warned people not to touch the items because they might have sharp edges, but Matney said no hazardous chemicals are aboard the satellite.

But there is plenty the trackers don’t know about the satellite’s re-entry – namely, where those pieces will fall – and that’s what spooks some people.

“There is no modeling that predicts where it will hit the surface of the Earth,” Duncan said.

Even at two hours before impact, when predictions by the Joint Space Operations Center will be “pretty accurate” in estimating where the craft’s orbit will lead, he said, that leaves an area covering thousands of miles where pieces could crash down. Weather and other factors could make a difference.

Kessler likens the satellite’s descent to a rock skipping across water: Rather than moving predictably, a craft leaving orbit skids across the upper portion of the atmosphere. That makes it difficult to know where the bits will fall until minutes before impact, he said.

Mike Weaver, an aerospace engineer at Aerospace Corp. in El Segundo, Calif., said the satellite may light up the sky for as long as two minutes as it makes its way from orbit.

Newer satellites are being designed for targeted re-entry, or to burn up completely before they hit the ground, said NASA’s Matney. The Chicken Little crowd need not worry too much on Friday, if the past is any predictor. “Most of these things fall in the water,” said Bill Ailor, another aerospace engineer at the company.

The Russian space station Mir fell safely into the South Pacific in March 2001. The U.S. space station Skylab disintegrated and tumbled into the Indian Ocean and sparsely populated parts of Australia in July 1979.

In fact, only one person is confirmed to have been hit by space junk over 50 years of space launches. In 1997, Lottie Williams, of Tulsa, Okla., was brushed by a small bit of metal mesh believed to have come from a spent Delta II rocket.

“I think I was blessed that it doesn’t weigh that much,” she told NPR in an interview that aired Wednesday. “That was one of the weirdest things that ever happened to me.”